Download May07 – 17 SCUBA Oxygen Analyzer

May07 – 17
SOAP: SCUBA Oxygen
Analysis Project
Team Members:
Advisor:
Michael Beckman
Adam Petty
Rory Lonergan
Jeffrey Schmidt
Dr. Gary Tuttle
Date Presented: 04-25-2007
Client:
Dan Stieler
Presentation outline
 Introduction
and project overview
 Project design
 Implementation and testing
 Resources and schedules
 Closing remarks
 Questions and answers
 Demonstration
Definitions and acronyms

Atmospheric pressure (ATM) - A measurement of pressure with 1 ATM
being the pressure at sea level.

Central nervous system (CNS) - Refers to the brain and spinal cord.

Maximum operating depth (MOD) - A SCUBA diving term referring to the
maximum safe depth based on the partial pressure of oxygen. While opinions
vary, the accepted safe maximum PO2 is 1.4 ATMs, with an absolute limit of
1.6 ATMs.

Nitrox - A gas mixture comprised of nitrogen, oxygen and other trace gases.
In SCUBA diving, Nitrox is commonly mixed to contain a higher than normal
percent of oxygen (greater than 20.9%).

Oxygen sensor - A device that measures the percentage of oxygen in a
gaseous medium using a chemical element.

PO2 - Partial pressure of oxygen, more accurately termed ppO2. PO2 is used
in the diving community for simplicity.

SCUBA - Acronym for self contained underwater breathing apparatus.
Acknowledgements

The team would like to thank their client, Dan
Stieler, for proposing this project. He provided a
great deal of insight into oxygen sensors and
analyzers and gave the team some great ideas
about how to design the device.

The team would like to thank the SSOL lab for
allowing the team to use their facilities and
equipment.
Introduction and
project overview
Problem statement (1/4)
 As
a diver descends, pressure increases
and more gas dissolves in the body
(Henry’s Law)
 As depth increases, more nitrogen
dissolves in the blood stream which must
be “off gassed” slowly on the way back to
the surface
 Failure to do so may cause
decompression sickness (the bends)
Problem statement (2/4)
 Partial
pressure of oxygen limits dive
depth and time
 Central
nervous system (CNS) oxygen
toxicity
 Maximum
PO2 of 1.4/1.6 ATMs
Problem statement (3/4)
 The
needed maximum operating depth
calculations are complex
 Tables
are commonly used, but can be
easily misread
Problem statement (4/4)
Goal:
Create a device to analyze and output the
percentage of oxygen in a SCUBA tank
while simultaneously outputting the
maximum operating depth
Problem solution (1/2)

Build a mobile oxygen analyzer that uses an
oxygen sensor.

This device takes the oxygen content of a
SCUBA tank as input and outputs the oxygen
percentage onto an LCD screen, along with the
MOD for the mixture.
Problem solution (2/2)
Operating environment

Since the device is used to analyze tanks both
indoors and outdoors, it was made to be water
resistant and to operate in a wide range of
climates.
 This device is not water proof.
 It is not guaranteed to operate correctly in
temperatures above 104° F or below 32° F.
 It was not designed to be able to survive
extreme physical trauma.
Intended users

This device is intended to
be used by certified
SCUBA divers and people
that refill SCUBA tanks.

This will typically be a fully
certified adult trained to
handle and/or fill high
pressure oxygen
containers.
Intended uses

Users can use the device to determine two
things:



The percentage of oxygen content in a SCUBA tank.
The MOD for a SCUBA dive.
Users that aren’t interested in the MOD can use
the device like any other conventional oxygen
analyzer.
Assumptions





The parts required are affordable and are
commercially available.
The team has access to a SCUBA tank for testing.
All of the components operate at or above their
specifications.
The components needed to make the device are
capable of being powered by a battery.
The user will follow the device’s instructions and
not use the device in a manner that was
unintended by the team.
Limitations

The oxygen sensor must be capable of reading in oxygen
content of a SCUBA tank within 1% of the actual value.
 The MOD must be accurate for the full range of the
possible oxygen input (0% O2 – 100% O2).
 The device’s user must have a way to correct inaccurate
input (calibrate the device).
 The device needs to display the oxygen percentage and
the MOD on the LCD.
 The device needs to be mobile and battery powered.
 The cost of the device’s parts should not greatly exceed
$150.
 The oxygen sensor can only be used in temperatures
below 104° F and above 32° F.
 The oxygen sensor must be stored in an environment
where the temperature is below 122° F and above 32° F.
End product and deliverables
 A fully
functional oxygen analyzer that is
capable of outputting the oxygen
percentage of a SCUBA tank and the
maximum operating depth for a dive.
Project design
Present accomplishments
 Purchased
components
 Completed design
 Built a working oxygen analyzer
 Finished product testing
Approaches considered
 Computer

based
Pros
• More extensible

Cons
• Not as portable
 Portable

device
Pros
• Small, easier to carry
• Simpler more reliable design

Cons
• Fewer expansion options
Project definition activities

Client meetings
 Discussions with divers




Easy to use with gloves
Easy to calibrate
Low cost
Market research


Features of similar items
Prices of similar items
Nuvair O2 Quickstick
$ 249.99
OMS OX-AM
$ 359.99
Oxycheq Expedition
$ 299.00
Oxycheq Expedition-X
$ 329.00
Teledyne AD-300
$ 399.00
Teledyne MD-300
$ 530.00
Prices of similarly featured oxygen analyzers
Research activities

Microcontroller: Different microcontrollers were
researched to find which one could be
implemented quickest.





Built-in ADC preferable.
Didn’t have programmer board for TI microcontrollers.
Confusing documentation for many microcontrollers.
Good documentation and examples for Microchip
(PIC) microcontrollers.
Instrumentation amplifiers: Researched to see if
they could remove parasitic offsets.
Overall system design
Design activities: Flow restrictor


A restricting orifice is
needed to obtain a flow
rate of 1-2 liters per
minute
OxyCheq flow restrictor and sensor cap
Constant flow rate of gas
provides consistent
readings
Flow restrictor diagram
Design activities: Oxygen Senor



Oxygen sensors




R22D from Teledyne
Uses a chemical reaction to
produce a voltage based on the
percentage of O2 present
Accuracy: Within 1% under
nominal conditions
Output: 8 – 13 mV nominal
Shelf-life is 6 – 24 months
Response time: 6+ seconds
Operating environment
restrictions
Design activities: Amplifier

The amplifier is used to increase the voltage signal from
the oxygen sensor to something usable for the
microcontroller's ADC
The amplifier
Design activities: Microcontroller
The microcontroller performs the
following functions:
 Using its ADC to turn the oxygen
sensor’s voltage into a digital value
 Calculating the percentage of
oxygen and the MOD
PIC18F4520
microcontroller
MOD equation

Outputting the percentage of oxygen
and MOD to the LCD backpack
Design activities: LCD Backpack
Serial enabled LCD backpack

Receives the “output to
display on the LCD” data
from the microcontroller’s
serial-output pin and
reformats it so that the LCD
can understand it

Bridges the gap between the
microcontroller and the LCD
Design activities: LCD screen

The LCD screen
outputs the oxygen
percentage and MOD
at PO2s of 1.4 and
1.6 ATMs

The screen refreshes
every 1.5 seconds
Formatted output on the LCD screen
Design activities: Power

The device is powered by a 9V battery, with 5V
being used by each component in the device
 A voltage regulator was used to keep the voltage
going into each component at 5V
 An on/off switch is used to power up/down the
device
Power switch and voltage regulation circuit
Design activities:
Low battery detection

When the voltage going into all the device’s
components drops below 5V, a LED lights
up to indicate that the battery is low
Low battery detection circuit
Design activities:
End-product design
Current end-product design

Aluminum Enclosure

8” x 4” x 1.5”

Weighs about 1 pound

Sized to be easily
usable when a diver
has all his/her diving
gear on – specifically
gloves
Implementation and testing
Implementation activities


Programmed microcontroller
Laid out, tested, and integrated components on
breadboard


Soldered components onto protoboard
Altered enclosure to house the protoboard, LCD
screen, power switch, sensor connection port,
etc

Integrated protoboard and components into the
enclosure

Integrated sensor with the device

Sensor is detachable and replaceable
Testing activities: Components

Microcontroller function testing




Low battery testing




Within function bounds
At function edges
Outside of function bounds
LCD
Microcontroller
LED
Sensor


Linear output over full range
Accurate within 1% of full scale
Testing activities:
End product (1/2)
 Testing




procedure
Took device to Microelectronics Research
Center
Plugged into SCUBA tank with regular air
(20.9% oxygen) and calibrated device
With oxygen and nitrogen tanks, used flow
regulators to create Nitrox with a specific
oxygen content
Allowed for end-product testing at different
oxygen levels
Testing activities:
End product (2/2)

Testing results:
Percentage O2
20.9
35.8
100

Voltage (mV) Linear (mV)
9.4
9.4
16
16.1014354
44.87
44.9760766
Expected % O2
33.1
35.8
50
Issue: Device has trouble operating
around 100% O2 due to a design flaw.
Measured % O2
33.3
36.2
50.2
Resources and schedules
Resources: Personnel
Michael Beckman (188 hours)
Rory Lonergan (173 hours)
Jeff Schmidt (197 hours)
Adam Petty (192 hours)
Member Advisor Mtg Group Mtg Other
Jeff
24
54
Rory
19
58
Michael
25
58
Adam
25
56
Total
93
226
Total
119
96
105
111
431
197
173
188
192
750
Resources:
Financial requirements
Parts
Wires, Cables, Connectors
ADC and Microcontroller
Pspice Simulation Software
DC Power Supply
Soldering Iron
Multi-meter or Oscilloscope
Computer
Microcontroller Programmer
Microcontroller Programming Software
Resistors, Capacitors, Op-Amps
Prototyping Boards
LCD Screen
Oxygen Sensor
Enclosure
Knobs and Buttons
Batteries
Poster
Miscellaneous (RTV Silicone)
Total
Labor
Total With Labor
Status
Provided
Purchased
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Purchased
Purchased
Purchased
Purchased
Provided
Provided
Purchased
Original Price Prediction
$10.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$5.00
$10.00
$15.00
$70.00
$20.00
$15.00
$0.00
$40.00
$40.00
$225.00
$8,536.00
$8,761.00
Modified
$0.00
$11.65
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$32.90
$70.00
$20.00
$15.00
$0.00
$15.00
$5.00
$169.55
$8,129.00
$8,298.55
Resources: Other
Requirement
DC Power Supply
Microcontroller Programmer
Soldering Iron
Multi-meter or Oscilloscope
Computer
Pspice
Microcontroller programming suite
Poster
Miscellaneous
Status
Provided
Provided
Provided
Provided
Provided
Provided
Provided
Purchased
Purchased
Price
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$0.00
$15.00
$5.00
Project schedule
Deliverable schedule
Closing remarks
Project evaluation
Milestones
Relative Importance
Evaluation Score
Resultant Score
Problem Definition
10%
100%
10%
Research
15%
100%
15%
Technology Selection
5%
100%
5%
End-product design
15%
90%
13.5%
Prototype implementation
15%
100%
15%
End-product testing
10%
90%
9%
End-product documentation
5%
90%
4.5%
Project reviews
5%
100%
5%
Project reporting
10%
95%
9.5%
End-product demonstration
10%
100%
10%
Total
100%
96.5%
Commercialization
 Estimated
cost to manufacture: $160
 Market pool is small
 Markup is generally around 100%
 MSRP of $300 with negotiable wholesale
price based on quantity sold
Recommendations
for future work
 Allow


use of additional sensors
Oxygen sensors other than R22D
Sensors for other gases
 Make
more water proof
 Improve battery accessibility
 Add metric measurements
 Testing in wider temperature range
 Eliminate need for LCD backpack
Lessons learned
 Establishing
a set time and location to
consistently work on the project
 Planning ahead on parts orders
 Ordering extra parts in the event of part
failure.
 Choosing technologies that are commonly
used and have documentation readily
available.
Unanticipated risks encountered
 Part
failure: Oxygen sensor,
microcontrollers, amplifiers


Using extreme care with parts
Ordering extra parts when feasible
 Incorrect
part order: Potentiometer,
microcontroller

Ordered several alternatives of each
component
Closing summary
 A mobile
oxygen analyzer capable of
displaying maximum operating depth
Questions?